The present invention relates to a high-speed silver halide emulsion having a high storage stability before and after exposure and a high resistance to damage by pressure, and a silver halide photographic light-sensitive material using the emulsion.
The basic performance required of a silver halide emulsion for a photographic light-sensitive material is to have a high sensitivity, a low fog, and fine grains.
To raise the sensitivity of an emulsion, it is necessary to (1) increase the number of photons absorbed by one grain, (2) raise the efficiency by which photoelectrons generated by light absorption are converted into silver clusters (latent image), and (3) raise the development activity in order to effectively use the generated latent image. As one countermeasure, increasing the size of a grain increases the number of photons absorbed by one grain, but this degrades the graininess. Also, the number of absorbed photons in a color sensitization region can be increased by increasing the amount of a spectral sensitizing dye which is used. However, the sensitivity decreases due to desensitization caused by the use of a large amount of a dye. In addition, although raising the development activity is an effective means for raising the sensitivity, this generally degrades the graininess in parallel type development such as color development. To increase the sensitivity without degrading the graininess, it is most preferable to raise the efficiency by which photoelectrons are converted into a latent image, i.e., raise the quantum sensitivity. To raise the quantum sensitivity, it is necessary to minimize an inefficiency factor, such as recombination or latent image dispersion, when photoelectrons are converted into a latent image. As one means, a method of reduction sensitization in which a small silver nucleus having no development activity is formed in the interior or on the surface of a silver halide grain is known to be effective to prevent recombination.
James et al. have found that when a coating film of an emulsion subjected to gold-sulfur sensitization is vacuum-deaerated and reduction-sensitized by heat-treating the film in a hydrogen gas ambience, sensitization can be performed at a lower fog level than in common reduction sensitization (T. A. Badcock, P. M. Ferguson, W. C. Lewis and T. H. James, Photogr. Sci. Eng., vol. 19 (1), 49 (1975)). This sensitization method is well known as hydrogen sensitization and is effective as a laboratory-scale sensitizing means. Hydrogen sensitization is actually used especially in the field of astronomical photographic light-sensitive materials.
Attempts of reduction sensitization have been studied for a long time. Carroll, Lowe et al., and Fallens et al., have disclosed in U.S. Pat. No. 2,487,850, U.S. Pat. No. 2,512,925, and British Patent 789,823 that a tin compound, a polyamine compound, and a thiourea dioxide compound are useful as reduction sensitizers, respectively. In addition, Collier compared the properties of silver nuclei formed by various reduction sensitization methods in "Photographic Science and Engineering", Vol. 23, page 113 (1979). She used methods using, e.g., dimethylaminoborane, stannous chloride, hydrazine, high-pH ripening, and low-pAg ripening. Methods of reduction sensitization are also disclosed in U.S. Pat. Nos. 2,518,698, 3,201,254, 3,411,917, 3,779,777, and 3,930,867. JP-B-57-33572 ("JP-B" means Published Examined Japanese Patent Application) and JP-B-58-1410 and JP-A-57-179835 ("JP-A" means Published Unexamined Japanese Patent Application) have disclosed not only selection of reduction sensitizers but also methods of using reducing agents. Furthermore, techniques of improving the storage stability of a reduction-sensitized emulsion are disclosed in JP-A-57-82831 and JP-A-60-178445.
Also, as described in T. H. James, "The Theory of the Photographic Process", 4th ed., Macmillan, 1977, page 152, a mechanism in which a silver nucleus consisting of two atoms formed by reduction sensitization captures a hole and decomposes into a silver ion and an unstable silver atom, the thermally unstable silver atom decomposes into a silver ion and a conductor electron, and this electron contributes to latent image formation is considered as reduction sensitization. This mechanism can increase the sensitivity to a maximum of a double sensitivity.
Unfortunately, reduction-sensitized emulsions have various drawbacks that, e.g., the storage fog is unsatisfactory, the exposed latent image undergoes intensification, and the sensitivity decreases when a raw sample is applied with a pressure, and so improvements have been demanded. It is considered that all these drawbacks result from the decomposition of unstable silver nuclei generated by reduction sensitization. Accordingly, studies have been made to remove unstable silver nuclei near the surface of a grain. JP-B-58-1410 has disclosed a method by which an oxidizing agent is added after the addition of a reducing agent. This method has attempted to remove unnecessary silver nuclei near the surface of a grain by chemically oxidizing the nuclei after reduction sensitization is performed. Also, JP-A-2-222939 has disclosed a method of removing unnecessary silver nuclei by adding thiosulfonic acid.
Although the above drawbacks are more or less improved by these techniques, the improvements are still on an unsatisfactory level. Therefore, further improvements have been demanded.
On the other hand, JP-A-63-220238 and JP-A-1-201649 have disclosed tabular silver halide grains in which dislocation lines (a kind of linear lattice defects existing in crystal) are intentionally introduced. These publications describe that tabular grains in which dislocation lines are introduced have excellent photographic characteristics such as sensitivity and reciprocity compared to tabular grains having no dislocation lines, and that the sharpness and the graininess are improved when these tabular grains are used in a light-sensitive material.
Also, JP-A-5-341459 describes that a silver halide emulsion having a high sensitivity and an improved graininess, gradation, and fog can be obtained by tabular silver halide grains having 10 or more dislocation lines per grain in a peripheral portion of a grain.
As described above, tabular grains in which dislocation lines are introduced have favorable properties to improve the sensitivity and the image quality.
To further improve the sensitivity and the image quality, it is very preferable to perform reduction sensitization for tabular grains in which dislocation lines are thus introduced. Unfortunately, it cannot be said that the storage stability and the resistance to damage by pressure described previously of tabular grains of this sort are satisfactory, and so techniques of improving the grains have been demanded.